In the plastic molding industry, there is a large demand for pellets of synthetic plastics of the thermoplastic type. In many of such machines, an extrusion die is used having a plurality of orifices through which the plastic while hot is extruded. As the extruded plastic emerges from the die face, one or more moving knives cut the emerging plastic into small pellets. In some of these machines, the plastic is extruded into a fluid bath (generally water) to solidify the plastic as it emerges from the die orifices and thus facilitate cutting by the knives. The water bath may also be used as a means to extract the pellets from the casing which surrounds both extrusion die and the cutting knives.
One of the difficulties encountered in the prior art machines is that, regardless of whether the die face is curved (such as cylindrical) or flat, as the plastics emerge from the die orifices and the knife passes over them to cut the pellets, the plastic has a tendency to smear under the knife. The result is that in a short time, sufficient plastic has been built up on the die face to require the stopping of the machine in order to clean off the die face. This smearing action is a minimum for some plastics, but on plastics such as polyurethane and polypropylene, the smearing takes place very rapidly and thus the down-time of such machines may be excessive.
Accordingly, one of the unsolved problems in the prior art is to obtain a machine which will make pellets from all kinds of thermoplastics without the smearing effect.
Another difficulty with the prior art machines is that in order to make clean cuts, the knives are pressed against the die face by spring means or by a direct mechanical fastening, so that the knife edge bears with considerable pressure against the die face. As a result, wear occurs, both on the knife and the die face which requires rather expensive regrinding and down time of the machine.